Heretofore, ball valves have been constructed so that the rotatable ball could be removed from the valve body for replacement or repair of the seat rings on opposed sides of the ball. Normally, a top or bottom cover plate has first been removed from the valve body and then the seat rings have been retracted and held in a retracted position until the ball is removed. Then the seat rings are removed.
For example, U.S. Pat. No. 3,114,386 dated Dec. 17, 1963 illustrates a so-called top entry ball valve in which an upper cover plate is first removed and then the spring urged seat rings on opposed sides of the ball in U.S. Pat. No. 3,114,386 are pushed manually to a retracted position. The seat rings are then held in the retracted position by pins fitting in annular grooves of the seat rings. With the seat rings retracted, the ball is removed and then the seat rings may be released and removed from the valve body.
When a valve is not in a line, the ends of the flow passage are open and a tool may be inserted in the open ends to grip the seat rings in some manner for pulling the seat rings to a retracted position. However, with the valve in place within a flowline the ends of the flow passage are closed and it is very difficult if not impossible to push the spring urged seat rings back to a retracted position where they may be retained. A relatively long travel is required for floating seat rings in a top entry ball valve to permit the seats to retract a sufficient distance for removal of the ball and the spring forces urging the seat rings toward the ball are relatively high in order to provide an adequate spring force at the extended position of the seat rings when in sealing engagement with the ball.